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| United States Patent |
5,091,880
|
|
Isono
, et al.
|
February 25, 1992
|
Memory device
Abstract
A memory device comprises a base plate with a memory element supporting
layer, a probe with a pointed tip portion, and a fine scan element for
causing the probe to scan over the surface of the memory element
supporting layer. When the probe is approached to the surface of the
memory element supporting layer and a suitable bias voltage is applied
across the probe and the memory element supporting layer, a tunnel current
is cause to flow therebetween and a specific region of the surface of the
supporting layer is excited. The excited region can adsorb one molecule
of, for example, di-(2-ethylhexyl)phthalate. By causing the memory element
to be adsorbed selectively on the memory element supporting layer, data is
recorded in the form of a projection-and-recess pattern. The recorded data
can be read out by observing the surface configuration of the supporting
layer in accordance with the principle of an STM (scanning tunneling
microscope).
| Inventors:
|
Isono; Yasuo (Fussa, JP);
Kouchi; Toshihito (Tama, JP);
Toda; Akitoshi (Kunitachi, JP);
Kajimura; Hiroshi (Tokyo, JP);
Mimura; Yoshiyuki (Hachioji, JP);
Ohta; Hiroko (Hachioji, JP);
Shimizu; Ryouhei (Koshigaya, JP)
|
| Assignee:
|
Olympus Optical Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
471841 |
| Filed:
|
January 29, 1990 |
Foreign Application Priority Data
| Feb 02, 1989[JP] | 1-24554 |
| Feb 10, 1989[JP] | 1-32255 |
| Current U.S. Class: |
369/126; 977/DIG.1 |
| Intern'l Class: |
G11C 007/00; G11B 011/00 |
| Field of Search: |
365/151,174
369/126
|
References Cited
U.S. Patent Documents
| 4575822 | Mar., 1986 | Quate | 365/174.
|
| 4916688 | Apr., 1990 | Foster et al. | 369/126.
|
Other References
D. W. Abraham et al., "Surface Modification with the Scanning Tunneling
Microscope", IBM J. Res. Develop., vol. 30, No. 5, Sep. 1986, pp. 492-499.
U. Staufer et al., "Surface Modification in the Nanometer Range by the
Scanning Tunneling Microscope", J. Vac. Sci. Technol. A, 6(2), Mar./Apr.
1988, pp. 537-539.
|
Primary Examiner: Popek; Joseph A.
Attorney, Agent or Firm: Frishauf, Holtz, Goodman & Woodward
Claims
What is claimed is:
1. A memory device comprising:
a supporting member having a plurality of memory blocks, each of the memory
blocks including:
a recording medium provided on the supporting member;
a probe, supported in the vicinity of the recording medium, for writing
data on the recording medium or reading data therefrom;
scanning means for scanning the probe across the recording medium; and
a light-receiving element connected to the scanning means for activating
the probe to perform a data write/read operation upon receiving light; and
optical means for radiating light selectively on the light-receiving
elements of said memory blocks.
2. A memory device according to claim 1, wherein said supporting member
comprises a rotatable disk member, and said memory blocks are arranged
along a plurality of concentric circles on said disk member at a
predetermined pitch.
3. A memory device according to claim 2, wherein said optical means
comprises an optical head which is movable radially of the concentric
circles.
4. A memory device according to claim 1, wherein said optical means
comprises an optical pattern generator for radiating light onto the
light-receiving elements at one time.
5. A memory device according to claim 4, wherein said optical pattern
generator comprises an optical mask.
6. A memory device according to claim 4, wherein said optical pattern
generator comprises a photographic projector.
7. A memory device according to claim 4, wherein said optical pattern
generator comprises a hologram image generator.
8. A memory device comprising:
a supporting member having a plurality of memory blocks, each of the memory
blocks including:
a recording medium comprising a substantially flat portion of the
supporting member;
a probe, supported in the vicinity of the recording medium, for writing
data on the recording medium or reading data therefrom;
scanning means for scanning the probe across the recording medium; and
a light-receiving element connected to the scanning means for activating
the probe to perform a data write/read operation upon receiving light; and
optical means for radiating light selectively on the light-receiving
elements of said memory blocks.
9. A memory device according to claim 8, wherein said supporting member
comprises a rotatable disk member, and said memory blocks are arranged
along a plurality of concentric circles on said disk member at a
predetermined pitch.
10. A memory device according to claim 9, wherein said optical means
comprises an optical head which is movable radially of the concentric
circles.
11. A memory device according to claim 8, wherein said optical means
comprises an optical pattern generator for radiating light onto the
light-receiving elements at one time.
12. A memory device according to claim 11, wherein said optical pattern
generator comprises an optical mask.
13. A memory device according to claim 11, wherein said optical pattern
generator comprises a photographic projector.
14. A memory device according to claim 11, wherein said optical pattern
generator comprises a hologram image generator.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a memory device having an uneven pattern.
2. Description of the Related Art
With a recent development of an information-oriented society, the amount of
data processed in computers increases more and more. To meet the demand
under the circumstances, various types of large-capacity memories such as
16 M bit DRAMs or optical disc memories have been developed. Also, it is
required that the memories be accessed at high speed for high-speed data
processing.
In order to increase the memory capacity of a recording medium, it suffices
if the size of the recording medium is increased. However, if the size of
the recording medium increases, there occur electrical problems such as an
increase in parasitic capacitance or parasitic inductance, and mechanical
problems such as an increase in range of operation. Consequently, the
access speed of the memory decreases. Under the circumstances, the
reduction in size of the memory has been developed for attaining the
high-speed memory access.
For example, the access speed of the memory using electric circuits is
increased by integrating the circuits on a semiconductor substrate. Also,
the high-speed memory access of an optical disc memory is achieved by
reducing the size of a data record region (memory pit) and increasing the
density of memory pits. However, the reduction in size of the memory and
the increase in access speed by means of these techniques are close to the
limits.
In general, in the memory using electric circuits, a lithographic method is
used to form a design pattern on a semiconductor substrate. In this
method, the finer the design pattern becomes, the less ignorable the
interference of light (electromagnetic wave) radiated from a light source
becomes. As a result, the reduction of the width of wiring lines is
limited. On the other hand, in the optical disc memory, memory pits are
formed, for example, by radiating a laser beam with a small diameter onto
a material, thereby forming pits with an uneven configuration or changing
physical properties such as reflectivity or refractive index. In this
case, too, the reduction of the diameter of a beam is limited by the
interference of light (laser beam), and accordingly the reduction of the
size of each memory pit is limited.
A scanning tunneling microscope (STM) is known as a surface observation
device with high resolution. When a pointed tip of a metal probe is
approached to the surface of a workpiece at a distance of about 1 nm, and
a voltage is applied across the probe and the workpiece, electrons are
allowed to flow through a gap (tunnel effect), which was considered
impossible from the view-point of classical mechanics, and a tunnel
current flows therebetween. The ST takes advantage of this tunnel effect.
The probe is moved in three-dimensional directions while detecting the
tunnel current to observe the surface configuration of the workpiece. The
resolution of the STM is about 0.1 nm, and the atomic arrangement of the
surface of the workpiece can be observed. It has been proposed that a
memory be manufactured according to the principle of the STM with high
resolution.
U.S. Pat. No. 4,575,822 (to Quate) discloses a method and an apparatus for
recording data, wherein a voltage is applied across an electrically
conductive probe and a substrate capable of holding electric charge, and
perturbation is caused in the substrate by a tunnel current flowing
therebetween. Data is recorded in accordance with the presence/absence of
the perturbation. Since this method utilizes the variation in work
function of the substrate due to an electric field, the size of a memory
bit is considerably greater than that of an atom. For example, in the case
of a substrate with a capacitance of 1 mF per 1 cm.sup.2, the density of
charge becomes 10.sup.-8 /.ANG..sup.2, when the potential of charge in the
substrate is set to 10 mV or more to avoid thermal disturbance. In other
words, the area affected by an electric field of one electron, i.e. the
size of a memory pit, is 10.sup.8 .ANG..sup.2. Thus, the atomic-level
resolution of the STM is not fully utilized.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a memory in which the
recording density is increased while the access speed is not decreased.
A memory device according to the invention comprises a supporting member
having a plurality of memory blocks. Each of the memory blocks including a
recording medium provided on the supporting member, a probe, supported in
the vicinity of the recording medium, for writing data on the recording
medium or reading data therefrom, means for scanning the probe across the
recording medium, and a light-receiving element connected to the scanning
means for activating the probe to perform a data write/read operation upon
receiving light. The memory device according to the invention further
comprises optical means for radiating light selectively on the
light-receiving elements of the memory blocks.
Additional objects and advantages of the invention will be set forth in the
description which follows, and in part will be obvious from the
description, or may be learned by practice of the invention. The objects
and advantages of the invention may be realized and obtained by means of
the instruments and combinations particularly pointed out in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part
of the specification, illustrate presently preferred embodiments of the
invention, and together with the general description given above and the
detailed description of the preferred embodiments given below, serve to
explain the principles of the invention.
FIG. 1 shows a basic structure of a memory of the present invention;
FIG. 2 is a perspective view showing a fine scan element shown in FIG. 1;
FIG. 3 shows a memory device wherein a number of memory blocks are arranged
on a single recording disc;
FIG. 4 shows a basic structure of the memory block arranged on the
recording disc shown in FIG. 3;
FIG. 5 is a block diagram showing a circuit for accessing a specific memory
block on the recording disc shown in FIG. 3; and
FIG. 6 shows another embodiment of a memory device wherein a number of
memory blocks are arranged on a single board.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will now be described with
reference to the accompanying drawings.
As shown in FIG. 1, a memory according to the present invention basically
comprises a base plate 10, a probe 18 and a fine scan element 20. The base
plate 10 comprises a substrate 12 and a memory element supporting layer
14. The probe 18 is supplied with a suitable bias voltage. The fine scan
element 20 causes the probe 18 to move in three-dimensional directions.
Any type of substrate 12 may be used, if it can support the memory
supporting layer 14. The substrate 12 may be dispensed with, if the memory
element supporting layer 14 itself has sufficient strength. In this case,
the layer 14 itself may be used as a substrate.
Data is recorded such that a memory element 16 is adsorbed selectively on
the base plate 10 (more specifically, the memory element supporting layer
14). Data is erased such that the memory element 16 is removed from the
base plate 10. A method of adsorbing/removing the memory element 16
on/from the base plate 10 was disclosed by J. S. Foster et al. in NATURE,
vol 331, page 324, 1988. According to this method, one molecule of
di-(2-ethylhexyl) phthalate can be adsorbed on a specific region of the
surface of a graphite base plate excited by means of a tunnel current.
Also, the adsorbed molecule of di-(2-ethylhexyl) phthalate is removed by
applying a suitable bias voltage to the probe.
Since data is recorded on the memory element carrying layer 14 in the form
of projections and recesses at the order of molecules, it is necessary
that the surface of the memory element supporting layer 14 have exact
flatness. Unevenness of the surface of the base plate adversely affects
the S/N of data reading. Thus, a monomolecular film of graphite, metal or
organic material, which ensures excellent flatness, may be used as the
memory element supporting layer 14. In particular, an LB film formed by
means of a Langmuir-Blodgett's technique (LB technique) is desirable. The
LB film has a structure wherein monomolecular films of chain molecules of
hydrocarbon, each having hydrophobic property at one end and hydrophilic
property at the other, are regularly arranged. Theoretically, the surface
of the LB film has a flatness of molecular order. A high S/N can be
ensured by the use of the LB film.
The memory element 16 comprises an aggregate of molecules of one or more
chemical substances. Desirable chemical substances are di-(2-ethylhexyl)
phthalate, benzen, TTF-TCNQ, phthalocyanine, liquid crystal compound, and
protein. When the molecule of a chemical substance is used as the memory
element 16, the size of a memory pit can be reduced to the size of one
molecule at a minimum. For example, if the molecule of di-(2-ethylhexyl)
phthalate is used as the memory element, the size of the memory pit is 4
.ANG..times.4 .ANG.. Accordingly, the recording density becomes very
higher, and the memory capacity increases. Namely, it is possible to
obtain about 10.sup.8 times the memory capacity of a currently available
optical disc memory.
If the memory element supporting layer 14 is formed of an organic LB film
and the memory element 16 is formed of an organic substance so that the
characteristics of both are made similar to each other, the adsorption and
removal of the memory element 16 on/from the base plate 10 becomes easier.
Also, if the memory element 16 is attached to the base plate 10 by means
of chemical bonding or polymerization, natural removal of the memory
element 16 can be prevented for a long time. This type of memory device is
applicable to a ROM which must have high durability.
A tip portion of the probe 18 has a radius of curvature of about 0.1 .mu.m,
and it is desirable that at least 1 .mu.m of the tip portion be tapered.
The probe may be manufactured by means of electropolishing, like a probe
used for a field emission microscope, or it may be manufactured by means
of mechanical polishing.
The fine scan element 20 is an actuator for microscopic positional control
and scanning of the probe 18. The fine scan element 20 is formed of, e.g.
piezoelectric material. FIG. 2 shows an example of the fine scan element
20. Piezoelectric elements 24 and 26 are arranged with an electrode
interposed therebetween. Two electrodes 28 and 32 are formed in an upper
surface portion of the piezoelectric element 24, and two electrodes 30 and
34 are formed in a lower surface portion of the piezoelectric element 26.
The probe 18 is disposed at a front middle portion of the fine scan
element 20. The probe 18 is connected to an STM (scanning tunneling
microscope) drive circuit through a line 36. For example, when an electric
field is applied to the piezoelectric elements 24 and 26 in a direction
from electrode 28 to electrode 30, the piezoelectric elements 24 and 26
extend in the direction of the X-axis (shown in FIG. 2). By virtue of this
property, a suitable voltage is applied to the electrodes 22, 28, 30, 32
and 34 so that the fine scan element 20 can be moved (or scanned) in
three-dimensional directions. The relationship between the intensities of
electric field vectors E1, E2, E3 and E4 and the scan direction of the
fine scan element 20 is as follows:
X: Positive Direction E1=E2=E3=E4>0
Negative Direction E1=E2=E3=E4<0
Y: Positive Direction E1=E2>E3=E4
Negative Direction E1=E2<E3=E4
Z: Positive Direction E1=E2<E3=E4
Negative Direction E1=E2>E3=E4
The data read operation of the memory will now be described. The tip
portion of probe 18 is caused to approach the surface of base plate 10 at
a distance of about 1 nm. A bias voltage is applied across the probe 18
and the base plate 10, so that a tunnel current flows therebetween. The
tunnel current changes delicately in accordance with the distance between
the tip of probe 18 and the base plate 10. The projections and recesses of
the surface of base plate 10, i.e. recorded data, can be read by virtue of
this property of the tunnel current. For example, the probe is caused to
scan over the surface of the base plate by means of the fine scan element
20, while the distance between the probe and the base plate is being
adjusted to keep the tunnel current constant. In this case, the tip
portion of the probe moves over the uneven surface of the base plate at a
predetermined distance from the surface of the base plate. On the basis of
the voltage applied to the fine scan element 20, an image of an uneven
surface representative of the configuration of the surface of the base
plate can be obtained. Thus, the unevenness of the surface of the base
plate is read out as recorded data.
FIG. 3 shows a memory device wherein a plurality of memories are provided
on a single disc. The memory device comprises a recording disc 40 with
memory blocks 38, and an optical head 42 for selecting a given memory
block 38. As schematically shown in FIG. 4, each memory block 38 comprises
a pair of a fine scan element 20 and a base plate 10, and a
light-receiving element 44 for starting a write/read operation upon
receiving a light beam of a specific wavelength. The memory blocks 38 are
arranged, for example, concentrically with a predetermined pitch. A given
memory block 38 can be accessed by designating a track number and a sector
number.
The optical head 42 is movable in the radial direction of the recording
disc 40. A laser beam source 46 of the optical head 42 emits, in a
pulsating manner, a detection light beam for detecting the position of a
target memory block 38 and a drive light beam for performing a write/read
operation having a wavelength different from that of the detection light
beam. The detection light beam emitted from the laser beam source 46 is
reflected by a half-mirror 48 and converged on the recording disc 40 by a
first converging lens 50. The disc 40 has a mirror face in regions where
the memory blocks 38 are not disposed, and the mirror face reflects the
detection beam almost completely. The detection beam reflected by the
recording disc 40 returns to the half-mirror 48 through the first
converging lens 50. Half the detection beam is reflected by the
half-mirror 48, and the other half passes through the half-mirror 48. The
beam component, which has passed through the half-mirror 48, is guided
through a second converging lens 52 to a received-light detector 54 for
accessing a target memory block 38.
The operation for accessing the target memory block 38 will now be
described with reference to FIG. 5. The recording disc 40 is rotated at a
predetermined angular speed by a motor 56. The optical head 42 is moved in
the radial direction (e.g. radially outward direction) of the recording
disc 40, while it radiates the detection beam onto the disc 40. In this
case, the intensity of the detection beam input to the received-light
detector 54 varies in a pulse-like manner when the beam crosses the track
of the memory block 38. The change in intensity of the detection beam is
detected by the received-light detector 54, and the number of pulses is
counted by a counter 58. The positional data (track number and sector
number) of the memory block 38 to be accessed is input in advance from a
keyboard 60 and is processed in a CPU 62. Thus, the number of the track
above which the head 42 is to be fixed is determined. An optical head
drive circuit 64 is controlled by the CPU 62, and the operation of the
drive circuit 42 is stopped when the count value of the counter 58
indicates that the optical head 42 is located on the target track. Then,
the optical head 42 is fixed above the track. This optical head 42 detects
a home position recorded on the disc 40 track by track. Further, on the
same track, the intensity of the detection beam varies in a pulse-like
manner, when it passes the memory block 38. Thus, the number of pulses is
counted by the counter 58 as a sector number, beginning from the home
position. Consequently, the target memory block 38 is selected. When the
selected memory block 38 comes to the focal point of the optical head 42,
the laser beam source 46 emits a drive pulse beam of a specific
wavelength, in order to drive the light-receiving element 44. When the
light-receiving element 44 receives the beam of the specific wavelength,
the STM drive circuit 68 starts the data write/read operation in the
above-described manner. A number of memory blocks 38 on the disc 40 are
connected, block by block (e.g. track by track), to output lines 70. The
number of output lines 70 is the same as the number of blocks (e.g.
tracks). The output lines 70 are connected to conductors in a rotational
shaft (not shown) of the recording disc 40, and are led to an external
device through a mercury switch, a brush, or the like. In FIG. 5, although
the STM drive circuit 68 is connected in parallel to the memory blocks 38,
only a specific memory blocks 38 is operated since the light-receiving
element 44 is switched upon receiving the drive pulsatile beam.
The access speed of each memory block 38 is substantially equal to the read
speed in a conventional optical disc. The read speed in each memory block
38 is higher than the read speed in a conventional STM memory. The reason
for this is that, since the fine scan element 20 is manufactured very
finely in a semiconductor IC process, the mechanical operation range
becomes small, and the parasitic capacitance and parasitic inductance of
the electric circuits are decreased. As a result, the memory capacity can
be remarkably increased without lowering the access speed.
FIG. 6 shows another embodiment of the invention. As in the above
embodiment, each of a plurality of memory blocks 38 provided on a
recording board 72 has a light-receiving element 14. When the
light-receiving element 44 receives a beam of a specific wavelength, a
write/read operation is started. In this embodiment, an optical pattern
generated from an optical pattern generator 74 is projected on the
recording board 72, and one or more memory blocks 38 which have received
light on the basis of the optical pattern are simultaneously operated. An
optical mask (transparency), a photographic projector, a hologram image
generator or the like may be used as the optical pattern generator 74.
Since a plurality of memory blocks 38 can be simultaneously accessed, the
memory device of this embodiment is suitable for a parallel arithmetic
operation computer. In particular, since the parallel access function is
very advantageous in arithmetic operations of vector data, this memory
device is applicable to an image processing device, an associative
arithmetic operation device, an AI device, etc.
Additional advantages and modifications will readily occur to those skilled
in the art. Therefore, the invention in its broader aspects is not limited
to the specific details, representative devices, and illustrated examples
shown and described herein. Accordingly, various modifications may be made
without departing from the spirit or scope of the general inventive
concept as defined by the appended claims and their equivalents.
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